Here at CNMAT we often work with tactile transducers in large stage settings and this presents a number of technical challenges.  Composers tend to favor inexpensive, off-the-shelf consumer amplifiers and transducer/exciters that can be difficult to interface with professional audio equipment without distortion or damage.  The core issue here is that the consumer level amplifier typically expects a -10 dBV (0.316 volt RMS) signal while most professional equipment is capable of handling much higher signal voltages--typically up to +24 dBu (12.28 volts RMS).  When transducers are deployed in a professional context (connected to a mixer or stagebox) level matching between these two standards can be fraught with difficulty.  One can set the gain pot on the amplifier to try to match level or, alternatively, one can dial back the gain at the mixer to compensate, but in either case a slip of the finger can lead to overloading the amplifier to a damaging level.  In the best case, protection circuitry will kick in to shut down the amp; in the worst case, the amp is damaged beyond function.  Moreover, properly unbalancing and converting the signal from TRS or XLR can require a pile of adapters, each link of which introduces a point of failure.  After struggling with these problems for many years, we have built a simple passive device to address these problems.

The CNMAT PC-2410 does four things:

• accepts professional-level signals via XLR or TRS jacks

• pads those signals through a balanced H-pad to drop the signal level from +24, +12 or +4 dBu to the nominal -10 dBV

• unbalances & impedance matches that signal through a transformer

• then outputs that -10 dBV single-ended signal through RCA jacks.

This solves a number of problems for the composer while improving reliability of the setup.  The composer can rest easy that they can drive the signal out of the board or stagebox without overoading the amplifier inputs.  This allows them to run the amplifier turned all of the way up without encountering distortion and retaining the full range of motion on the mixer faders.  Components have been chosen to ensure a reasonably flat (+/- 1 dB) frequency response through the audio range and the PCB has been designed to accommodate a range of customizations.

All design and fabrication files are available on Github: